The present invention relates to an emergency off-switching arrangement and to an emergency off-switch for triggering an emergency switch-off function for a safety-related shutdown of an electrical device.
Emergency off-switches in terms of the present invention are used to enable an electrical device, such as an electrical machine, an industrial production plant or an electrical supply device, to be selectively shut down in case of an emergency or a dangerous situation. For this purpose, the emergency off-switches usually have an actuator which is red in color, most commonly a push-button, which is arranged against a yellow background, for example a yellow housing part. Due to the widespread shape of the actuating element at least in the past, such emergency off-switches are sometimes referred to as mushroom buttons.
For complex machine systems with several emergency off-switches or for systems with a mobile control unit which is detachable from a machine, adaptable emergency off-switches are increasingly desired. ‘Adaptable’ in this context means the ability for certain applications to put the emergency off-switch into an inactive state, in which it does not exercise its intended emergency switch-off function. An example of such an application is that of mobile programming panels for industrial robots, which are connected to a robot only during the programming stage and must be fitted with an emergency off-switch in accordance with relevant safety standards (ISO 13849-1). Once such a panel is no longer connected to the robot, it can usually no longer trigger the emergency switch-off function. It goes without saying that in such a case, the emergency off-switch must no longer be represented as such, as otherwise a user is lulled into a false sense of safety.
As an approach to this problem, DE 199 19 012 A1 discloses an emergency off-command device which in the de-energized state, i.e. in a state in which there is no connection to a plant or machine, appears neutral in color, and so is not perceived as an emergency off-switch. But as soon as a connection is made to a machine and an emergency switching-off function can be triggered via the emergency off-command device, the emergency off-command device assumes its characteristic coloring. For this purpose the emergency off-command device comprises, e.g., a transparent or translucent housing, which can be illuminated by means of colored lighting elements, such as color LEDs. With the activation of the command unit, the lighting elements are switched on and the emergency off-command device appears in a standard-compliant coloring.
As an alternative to the active illumination of the adaptable emergency off-switch, DE 103 44 385 A1 discloses another adaptable emergency off-switch, which in a rest position has the previously mentioned characteristic coloring and on being disabled via a passivation element, can be displayed in a visually neutral manner. Thus, for example, an LCD or TFT display on the housing of the emergency off-switch can cover the signal colors of the housing in the passive state. The advantage of this variant is that the emergency off-switch in the active state is not dependent on active illumination.
In both of the above variants, i.e. regardless of whether the emergency off-switch is actively illuminated or actively covered, there is a risk that the respective optical change fails to occur due to a fault. In other words, it may occur that an inactive emergency off-switch is displayed as active, or an active emergency off-switch is displayed as passive. It goes without saying that an incorrectly displayed emergency off-switch is associated with a significant safety hazard.